<!DOCTYPE html>
<style>
    body {
        margin: 0;
    }
    div.green {
        position: absolute;
        top: 100px;
        left: 100px;
        width: 100px;
        height: 100px;
        background: green;
    }
</style>
<body>
    <div class="green">
    </div>
</body>